There's a shader manual that comes with GtkRadiant. I know a lot of beginners hate it when they're pointed to it but when you make an effort to learn it and try to make some shaders on your own you can become a very powerful mapper

There arent any. That's because "shaders" is an incredibly expansive topic. Your best approach is to ask a question more specifically related to what you want your shader to do. From there, try finding a similar shader from the JA assets and look at its code. You can use the q3map2 shader manual to look things up.